Belzer et al U.S. Pat. Nos. 3,632,473 and 3,753,865 disclose a widely-accepted system for preserving organs such as kidneys for transplantation. Perfusate (plasma) is pumped in a series of regular pulses through a heat exchanger where it is cooled to a temperature of about 4.degree. to 8.degree. C. and is then delivered to an organ supported in a perfusion chamber. Since it is necessary for effective organ preservation that the perfusate be delivered to the organ in a series of regular pulses, such an exchanger must be of the type which will not appreciably dampen the pulsatile flow. Consequently, such an arrangement does not permit the use of an exchanger having an extended tubular heat-conductive coil into which the perfusate is pumped because any substantial length of tubing would have the effect of destroying the pulse wave.
Portable perfusion units have recently been developed in which pulsatile flow is maintained through the heat exchanger by pumping the perfusate into a compartment which is closed, except for an inlet (communicating with the pump) and an outlet (communicating with the organ in the perfusion chamber), so as to avoid damping out the pulses. Cooling is achieved by circulating cold water through a tubular coil disposed within the compartment. Such a system requires two pumps, one for the perfusate and the other for the water, an obvious disadvantage in terms of bulk, weight, and complexity, especially in a portable unit. Further, to achieve sufficient dwell time to cool the perfusate, the compartment must be of substantial size and the perfusate flow rate must be relatively low. Even so, appreciable differences may develop between the temperature of the water and the lowest temperature reached by the perfusate. For example, where ambient temperatures are relatively high, a temperature differential of 5.degree. or more may exist between the temperature of the ice water and that of the perfusate as it passes from the exchanger.